The construction industry is a colossal contributor to carbon dioxide (CO₂) emissions, accounting for a staggering 37% of energy- and process-related CO₂ emissions worldwide in 2021. Unfortunately, it's currently not on track to achieve decarbonization by 2050. However, a promising approach to tackle this challenge is emerging: the integration of CO₂ into construction materials through carbonation reactions. This innovative approach harnesses the natural chemical reactivity of certain alkaline materials with CO₂ to create durable building materials. These materials include metal hydroxides or oxides like CaOH, MgOH, CaO, and MgO, which, when combined with water, form ionic-bonded carbonate minerals such as CaCO₃ and MgCO₃. The beauty of this process is its versatility; it can utilize various materials, ranging from silicate mine residues and lime to industrial by-products like steel slag.

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The Carbon Fixing Process:

‍Carbonation can occur at different stages of material production:

• Material Production: The carbonation reaction can take place during the production of the material itself. Alternatively, it can occur during the hardening phase of the material. In this case, liquid CO2 is often injected into the process.
• Component Production: Carbonation can also happen during the production of one of the components of the final building material.

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Crucially, the CO₂ used must come from biogenic sources or direct air capture facilities, not from fossil fuels. Traceability of the CO₂ is essential to prove that a carbon dioxide removal (CDR) activity has occurred and to quantify its impact.  

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‍Potential and Scalability:

‍One of the significant advantages of carbonation reactions is that they chemically bind and mineralize carbon into the building elements as carbonates. This permanence means the risk of carbon release is very low. Moreover, the infrastructure and process technology required for producing carbon-rich building materials are, in principle, already in place. However, to enable large-scale adoption, sector-wide material norms and regulations need to adapt to accommodate these new materials. The good news is that carbonated building materials hold immense promise for scalability. Only limited adjustments are needed to incorporate the CO₂ fixing process into existing production processes. This ease of integration makes this approach particularly attractive for the construction sector, which grapples with many hard-to-abate emissions. While carbonating construction materials is a compelling solution, other methods also contribute to carbon negativity in construction materials. One such approach involves adding biochar to cement mixes, creating carbon sinks. In conclusion, the construction industry's carbon footprint is a pressing issue that demands innovative solutions. Carbonating construction materials present a sustainable path forward, with the potential to significantly reduce emissions and pave the way for a greener, more sustainable future in construction.